<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box1{
            width: 200px;
            height: 200px;
            background-color: red;
            transition:all 1s linear 1s;
            /*
              all    所有的属性
              2s     动画时间
              linear 匀速
              2s     延迟
              
              除了display:none / block 属性无法支持
            */
        }
        .box1:hover{
            height: 600px;
            background-color: yellow;

        }

        .box2{
            width: 200px;
            height: 50px;
            background-color: yellow;
            border: 1px solid gray;
            margin-top: 20px;
        }
        .box2 ul{
            /* display: none; */
            margin-top: 50px;
            transition: all 1s;
            height: 0px;      /*设置高度为0*/

            overflow: hidden; /*将溢出部分隐藏*/
        }
        .box2:hover ul{
            /* display: block; */
            height: 200px;    /*移入之后高度变换*/
        }
    </style>
</head>
<body>
    <div class="box1"></div>

    <div class="box2">
        我的菜单
        <ul>
            <li>1111</li>
            <li>2222</li>
            <li>3333</li>
            <li>4444</li>
            <li>5555</li>
        </ul>
    </div>
</body>
</html>